This present invention relates to the field of radiation curable polymers, particularly to acrylate terminated, radiation curable polymers useful for coatings. There have been many proposals for radiation curable coating polymers. Among the most commercially successful of such proposals are the epoxy acrylates, the polyester acrylates, and the urethane acrylates. Such acrylates have the advantages of having very low volatile organic compounds (VOC) as well as high productivity. Ultraviolet (UV) and electron beam (EB) are the most typical forms of radiation which are used to generate free radicals which initiate the polymerization or cure. While almost instant cure results in the high productivity, it also makes it difficult to achieve good adhesion, especially to difficult substrates such as polycarbonate (PC) and polyvinyl chloride (PVC). This problem is due in part to the lack of time for the cured matrix to relax.
Polycarbonate-containing acrylate-containing polymers having a single polycarbonate moiety have been suggested by Yamamoto, et al., U.S. Pat. No 5,178,952; Coqueugniot, et al., U.S. Pat. No. 4,255,243; Watson, Jr., U.S. Pat. No. 4,264,752 and Endo, et al., U.S. Pat. No. 5,143,997. However, such prior art polymers were not reported as having good adhesion or weathering properties.
It is an object of the present invention to provide radiation curable acrylic coating polymers which have adhesion properties on plastic substrates which are superior to the state of the art.
It is another object of the invention to provide polymers which can be UV or EB cured on plastic substrates and provide coatings which have excellent impact strength as well as adhesion properties.
These objects, and others which will become apparent from the following disclosure, are achieved by the present invention which comprises in one aspect a polymer of the formula (I)
(Acr)y(A)(Q)(PC)[(Q)(PC)]x(Q)(A)(Acr)yxe2x80x83xe2x80x83(I)
wherein
(Acr)y(A) is the residue of hydroxyalkyl acrylate or hydroxyalkyl methacrylate having an alkyl moiety, A, and where said alkyl, A, has 2 to 5 carbon atoms and wherein Acr is an acrylate or methacrylate moiety;
y is the number of acrylate or methacrylate groups linked to moiety A.
Q is the residue of one or more organic diisocyantes, which are connected with A via a urethane linkage;
PC is the residue of an alkylene diol polycarbonate of the formula (II)
HO(ROCOO)nROHxe2x80x83xe2x80x83(II)
R is one or more (C2 to C10) alkylene or one or more (C6 to C12) aromatic group;
y is an integer from 1 to 5;
x is from 1 to 20;
n is an integer from 1 to 10,000;
PC and Q are connected via a urethane group.
In another aspect, the invention comprises a process of preparing the polymers of formula (I) comprising reacting an alkylene or arylene diol polycarbonate with a molar excess of polyisocyanate to form urethane linkages, and then reacting the resultant isocyanato-functional polymer with a hydroxyalkyl acrylate or hydroxyalkyl methacrylate.
A still further aspect of the invention is a coating prepared by curing polymer of formula (I) by applying it to a substrate and curing in the presence of UV or EB radiation, the process of preparing the coating, and coated articles.
The polymers can be used alone or in combination with other free radically polymerizable materials such as allyl monomers and oligomers or (meth)acrylate monomers and oligomers. The coatings of the invention show excellent physical properties such adhesion, reverse impact strength, and weathering.
The polyisocyanates used in this invention can be aliphatic or aromatic with various number of isocyanate groups, preferably two or more isocyanate groups per molecule. Some examples of isocyanates are isophorone diisocyanate, toluene diisocyanate, 4,4xe2x80x2-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, 4,4xe2x80x2-methylenebis(phenyl isocyanate). The polyisocyanates can be dimers, trimers, and polymers in nature such as allophanates, isocyanurates, uretdiones, biurets, of hexamethylene diisocyanate and isophorone diisocyanate. Preferred polyisocyanates are diisocyanates mentioned above such as isophorone diisocyantes, hexamethylene diisocyanate, and toluene diisocyanate, 4,4xe2x80x2-dicyclohexylmethane diisocyanate.
The condensation reaction can be carried out with or without catalysts. Catalyzed reactions are preferred due to the short reaction time and less side products. Typical catalysts can be used are amines, tin-based catalysts. Some catalyst examples are dibutyltin dilaurate, 1,4-diazabicyclo[2.2.2]-octane (DABCO), 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU), N,N-dimethylcyclohexylamine (DMCA), tetramethyltin, tetrabutyltin, tetraoctyltin, tributyltin chloride, dibutyltin dichloride, dibutyltin oxide, dibutyltin diacetate, butyltin trichloride, dioctyltin dichloride, dioctyltin oxide, dioctylton dilaurate, dioctyltin diacetate. Other metal based catalysts are zinc, iron, bismuth, and zirconium complexes.
Hydroxyl containing (meth)acrylic esters can be monoesters or multifunctional esters. Some examples are hydroxyalkyl (meth)acrylates, pentaerythitol triacrylate, trimethyololpropane diacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxyethyl methacrylate, caprolactone modified hydroxy functional (meth)acrylate.
Polycarboante polyols can be aromatic or aliphatic and they can be prepared readily from diols as desribed well known in the art. Some examples are pentanediol based polycarbonatediol, cyclohexanedimethanol polycarbonatediol, hexanediol polycarbonatediol, ethylene glycol polycarbonatediol, propylene glycol polycarbonate diol, butanediol polycarbonatediol, and polycarbonate diol based on ethoxylated bisphenol A.